JP6101108B2 - Cement admixture and cement composition - Google Patents

Description

  The present invention relates to a cement admixture and a cement composition containing the cement admixture.

Hardened cement bodies such as mortar and concrete are hardened by the hydration reaction of the cement contained in the cement composition, but after hardening, stress acts and changes in temperature and humidity occur. Cracks may occur in the cured body.
The hardened cement body having cracks has a problem of causing water leakage and the like in addition to strength reduction and appearance deterioration.

  Therefore, in recent years, hardened cement bodies having a property of naturally closing cracks in the presence of moisture even when cracks occur after curing, that is, so-called self-healing have been studied. In order to obtain such a hardened cement body having self-healing properties, various cement admixtures are blended into the cement composition.

For example, Patent Documents 1 to 3 describe cement compositions in which an expansion material having an action of reacting with calcium hydroxide or the like in cement to generate insoluble crystals is blended.
Patent Document 4 describes a cement composition in which an aluminosilicate having swelling property is further blended in addition to the expansion material.
Patent Document 5 describes a cement admixture granulated by kneading a component such as an expansion material component, a latent hydraulic material, calcium oxide, cement, and water.
Patent Documents 6 and 7 describe a bone for a hardened cement body, in which a waterproofing agent / water-stopping agent / deterioration inhibitor such as water-soluble silicic fluoride is mixed with cement and loaded on a carrier made of a porous body. The materials are listed.

  That is, Patent Documents 1 to 7 include a component that reacts with a component in a cement composition in the presence of water to generate crystals or the like, or a component that expands when cracks occur in the hardened cement body. It is described that by adding a cement admixture to a cement composition, the cement composition is provided with a crack self-healing property capable of closing the crack and self-healing.

In Patent Documents 1 to 4, a material having high water absorption, swelling property, and high reaction activity with water, such as an expansion material and aluminosilicate, is mixed with a cement composition as it is, and the hardened concrete is cracked and self-healing. Giving. However, when a material having a high reaction activity with water, such as an expansion material, is directly mixed with a cement composition, the fluidity of fresh concrete or fresh mortar may be reduced.
In order to suppress such a decrease in fluidity, it is necessary to increase the amount of water-reducing agent, high-performance water-reducing agent, etc., but if the amount of water-reducing agent or high-performance water-reducing agent is increased, setting delay or There is a risk that strength will be reduced. In addition, there is a problem that costs for increasing water reducing agents, high performance water reducing agents, and the like are increased.

Patent Document 5 describes a cement admixture that is granulated by kneading a component having crack self-healing properties with cement. Patent Documents 6 and 7 describe admixtures in which a porous carrier is loaded with a component having crack self-healing properties.
By using a cracking self-healing component contained in the granulated body or supported on a carrier, a decrease in fluidity can be suppressed to some extent, but sufficient crack self-healing property cannot be obtained.

Japanese Patent No. 3658568 JP 2005-239482 A JP 2007-332010 A JP 2009-190937 A JP 2011-57520 A JP 2003-95715 A Japanese Patent No. 4285675

  In view of the above-described problems, an object of the present invention is to provide a cement admixture and a cement composition that can exhibit high crack self-healing properties without causing a decrease in fluidity.

The cement admixture of the present invention comprises a first admixture comprising alumina cement and calcium hydroxide are mixed and a second admixture comprising Portland cement and calcium sulfate, said first admixture is granulated It is a coating particle formed by adhering alumina cement and calcium hydroxide to the surface of a granule or carrier, and the second admixture is prepared by adhering Portland cement and calcium sulfate to the surface of the granule or carrier. Coating particles.

  In addition, in this invention, a granulated body means the particle | grains which a solid component exists from the surface to the inside by solidifying a solid component by mixing water and another solid component on predetermined | prescribed mixing conditions.

In the present invention, the first admixture and the second admixture may be mixed so that the molar ratio of SO ₃ to Al ₂ O ₃ is 0.09 or more and 3.56 or less.

  Moreover, the cement composition of the present invention contains the cement admixture.

  According to the present invention, it is possible to provide a cement admixture and a cement composition capable of exhibiting high crack self-healing properties without fear of lowering fluidity.

The graph which shows a water flow test result. The table | surface which shows the SEM photograph which shows the observation result of the sample surface by a scanning electron microscope-energy dispersive X-ray spectrometer (SEM-EDS), and an elemental analysis result. The table | surface which shows the SEM photograph which shows the observation result of the sample surface by SEM-EDS, and an elemental analysis result. The table | surface which shows the SEM photograph which shows the observation result of the sample surface by SEM-EDS, and an elemental analysis result. The graph which shows the result of a thermogravimetric differential thermal analysis (TG-DTA).

  Hereinafter, embodiments of the cement admixture and the cement composition of the present invention will be specifically described.

"Cement admixture"
First, the cement admixture of this embodiment will be described.
The cement admixture of the present embodiment is a cement admixture in which a first admixture containing alumina cement and calcium hydroxide and a second admixture containing Portland cement and calcium sulfate are mixed.

(First admixture)
The first admixture in the present embodiment contains alumina cement and calcium hydroxide.

《Alumina cement》
The first admixture of this embodiment contains alumina cement.
Examples thereof include alumina cement that satisfies the standards of the former JIS R 2511 “Alumina cement for refractory”.
Alumina cement is preferable because the hydration reaction (hardening) is fast and the strength of the admixture can be increased in a short time. And it is suitable for using together with calcium hydroxide for the following reasons.
That is, calcium hydroxide and alumina cement react in the presence of water to produce calcium aluminate hydrates such as hydrocalumite and hydrogarnet. Since this calcium aluminate hydrate reacts with sulfate ions (SO ₄ ²⁻ ) in the presence of water at the cracked site to produce expansive ettringite, the crack healing effect is further enhanced.
The sulfate ions can be supplied from cement or from calcium sulfate in the second admixture.

"Calcium hydroxide"
The first admixture of this embodiment contains calcium hydroxide.
As the calcium hydroxide source, for example, commercially available products such as special slaked lime, No. 1 slaked lime, No. 2 slaked lime that conform to JIS R 9001 “industrial slaked lime”, and the like can be used.
Among them, it is preferable to use special slaked lime, No. 1 slaked lime, etc., which are inexpensive industrial slaked lime having a CaO content of 70% by mass or more and a maximum particle size of 0.1 mm (100 μm) or less.
Each of the calcium hydroxides may be used alone or in any combination.

In the present embodiment, the first admixture may contain water in addition to the alumina cement and calcium hydroxide.
By containing water, solid components such as alumina cement and calcium hydroxide can be hardened and shaped easily.

In the present embodiment, the first admixture may contain other solid components or liquid components as necessary.
Examples of the other components include water repellents, water shielding agents, clay minerals (Na-bentonite, Ca-bentonite, sepiolite, attapulgite, talc, etc.), feldspar (anorthite, potash feldspar, soda feldspar, etc.), alum Stone, calcium phosphate, inorganic carbonate (sodium carbonate, sodium bicarbonate, calcium carbonate = limestone fine powder, magnesium carbonate, etc.), coal ash (fly ash, cinder ash), amorphous siliceous fine powder (silica fume, metakaolin, Inorganic powder materials such as sedimentary silica, silica gel, etc.), natural pozzolans (siliceous white clay, tuff, shirasu, etc.), silica stone powder, blast furnace slag powder and cement clinker coarse powder.
The other components can be used alone or in any mixture.

  The first admixture of the present embodiment is a particle in which water and solid components such as alumina cement and calcium hydroxide are mixed under predetermined mixing conditions to solidify the solid components and present solid components from the surface to the inside. The granulated body may be used.

  When the first admixture is a granulated body, alumina cement and calcium hydroxide can also be present inside the first admixture.

The method of making the first admixture a granulated material is not particularly limited. For example, a solid component such as alumina cement and calcium hydroxide is added with a granulating amount of water and kneaded. And a method of granulating the obtained kneaded material.
For granulation, for example, known kneading granulators, wet extrusion granulators, cylindrical granulators, tilting-roller type agitation granulators, twin-axis granulators, disk pelleters (pan pelletizers) A fluidized bed granulator, a swirling fluidized bed granulator, or the like can be used.
The granulation conditions such as the number of revolutions of the granulator, the granulation time, and the amount of water are preferably adjusted as appropriate according to the particle diameter of the intended first admixture.

The first admixture of the present embodiment is a coating particle in which a paste prepared by mixing the alumina cement, calcium hydroxide, and water is attached to the surface of a carrier such as sand or blast furnace slag particles, in addition to being formed as the granulated body. It may be.
In this case, unlike the granulated body, alumina cement and calcium hydroxide can be present only on the surface of the particles.

  The method of using the first admixture as the coating particle is not particularly limited. For example, a solid component such as alumina cement and calcium hydroxide is added with a granulating amount of water. Examples thereof include a method of producing a paste and mixing the paste with a carrier to obtain concrete particles having the paste attached to the surface of the carrier.

(Second admixture)
The second admixture in the present embodiment contains Portland cement and calcium sulfate.

《Portland cement》
The second admixture of this embodiment contains Portland cement.
Examples of Portland cement include various Portland cements defined in JIS R 5210 “Portland cement”, such as normal, early strength, very early strength, moderate heat, low heat, very early strength, and sulfate resistance.
The Portland cement, are included aluminate _{(3CaO · Al 2 O 3,} 4CaO · Al 2 O 3 · Fe 2 O 3), can be together with the calcium sulfate, stably generate inflatable ettringite It becomes.

<Calcium sulfate>
The second admixture of this embodiment contains calcium sulfate.
Examples of the calcium sulfate source include general industrial gypsum such as anhydrous gypsum, dihydrate gypsum, and hemihydrate gypsum. The industrial gypsum is either a natural product or a by-product (by-product gypsum during flue gas desulfurization, by-product gypsum during hydrofluoric acid production, by-product gypsum during phosphoric acid production, by-product gypsum during titanium oxide production, etc.). May be.
Among these, anhydrous gypsum is preferable because it does not contain moisture and is easily pulverized.
The calcium sulfate may be used alone or as a mixture in any combination.

In the present embodiment, the second admixture may contain water in addition to the Portland cement and calcium sulfate.
By containing water, solid components such as Portland cement and calcium sulfate can be easily solidified as in the first admixture.

  In the present embodiment, the second admixture may contain other solid components or liquid components similar to the first admixture as necessary.

Similarly to the first admixture, the second admixture of the present embodiment may be a granulated body or a coating particle.
When the first admixture is a granulated body, the second admixture is also preferably a granulated body. When the first admixture is a coating particle, the second admixture is also a coated particle. It is preferable that

In the cement admixture of this embodiment, the first admixture and the second admixture are mixed.
Mixing ratio of the first admixture with a second admixture, the molar ratio of SO ₃ Al ₂ O ₃ and SO ₃ contained in the cement admixture, for _{Al 2 O 3 (SO 3 /} Al 2 O 3) The ratio is preferably 0.09 or more and 3.56 or less.

By molar ratio of SO ₃ for Al ₂ O ₃ in admixture falls within the above range, higher crack self-healing effect can be exhibited, and efficiently react with water occurs at the time of cracking, contribute to cracking healing Inflatable ettringite and the like are preferable because they are efficiently produced.

"Cement composition"
Next, the cement composition containing the cement admixture of this embodiment will be described.
The cement composition of this embodiment is a cement composition such as a mortar composition or a concrete composition.

  The cement composition of the present embodiment includes the cement admixture of the present embodiment described above and cement, and includes aggregates such as fine aggregate and coarse aggregate, water, and various other additives as necessary. You may go out.

"cement"
Although it does not specifically limit as said cement, Portland cement, the mixed cement based on Portland cement, a super-hard-hardening cement, other well-known cements, etc. are mentioned.

"aggregate"
As the fine aggregate, land sand (mountain sand), sea sand, river sand, crushed sand, quartz sand, blast furnace slag fine aggregate, ferronickel slag fine aggregate, copper slag fine aggregate, electric furnace oxidation slag fine aggregate, Examples include ferrochrome fine aggregate, artificial light-weight fine aggregate, recycled fine aggregate, and molten slag fine aggregate.
Examples of the coarse aggregate include land gravel (mountain gravel), sea gravel, river gravel, crushed stone, blast furnace slag coarse aggregate, artificial lightweight coarse aggregate, recycled coarse aggregate, molten slag coarse aggregate and the like.
Note that coarse aggregates and fine aggregates can be distinguished in accordance with the screening test of JIS A 1102.

  The amount of the fine aggregate and coarse aggregate contained in the cement composition of the present embodiment is preferably adjusted as appropriate according to the intended cement composition.

《Cement admixture》
The amount of the cement admixture contained in the cement composition of the present embodiment is, for example, ^{30 to} 600 kg, preferably 50 to 500 kg per 1 m ^{3 of} mortar hardened body in the case of a cement composition for mortar. Further, when the cement composition of the concrete cured body, the concrete hardened body 1 m ³ per 50～1000Kg, preferably 70～700Kg.

"water"
The cement composition of this embodiment may contain water.
The amount of the water is appropriately adjusted and blended, for example, according to the cement, the cement admixture, and if necessary.

  The hardened cement obtained from the cement composition of the present embodiment can self-heal such cracks even when cracks occur, for example.

  That is, in this embodiment, since the cement admixture in which the first admixture containing alumina cement and calcium hydroxide and the second admixture containing Portland cement and calcium sulfate are used, the cement hardened body is used. When cracking occurs, first, in the presence of water, the alumina cement and calcium hydroxide in the first admixture react to form calcium aluminate hydrate, and the calcium aluminate hydrate is Cracks can be blocked by generating expansive ettringite by reacting with calcium sulfate in the second admixture.

The cement admixture or cement composition of the present embodiment is, for example, a concrete viaduct superstructure, floor slab bottom and pier / abutment side, tunnel lining concrete, concrete bottom and side such as agricultural waterway, office building or apartment, etc. Slabs and walls, tunnel segments, box culverts, retaining wall products such as L-shaped retaining walls, U-shaped structures, fume pipes, utility poles, concrete blocks, concrete panels, etc. It can be suitably used for structures that have been difficult to repair.
When cracks occur in these structures and water is supplied to the cracked parts by rainfall, snowfall, groundwater infiltration, river water, seawater flow, water spraying, water injection operation, etc. This cement admixture causes a hydrate formation reaction with water and components in the cement, thereby effectively self-healing cracks.

In the case where cracks occur in the structure as described above, conventionally, repair work in which an organic or inorganic filling material is injected into the cracks is performed, or even if cracks occur, the structure is not affected. In some cases, measures such as waterproofing and waterproofing were applied to the hardened cement. However, such repair work, waterproof work, water stop work, etc. are costly, and if waterproof work or water stop work is performed simultaneously with the hardened cement construction work, the construction period of the structure will be prolonged. . In particular, if the mortar or hardened concrete is a structure such as a tunnel, a railway viaduct, or an automobile viaduct, repair work for these cracks after the start of service of the structure may result in traffic closure or suspension of service, etc. It was necessary and very difficult.
Therefore, when the cement admixture and cement composition of this embodiment are used in such a structure, the crack self-healing material performance can be obtained without performing repair work, waterproof work, water stop work, etc. as described above. There is an advantage that can be obtained.

  Since the cement admixture or cement composition of the present embodiment can exhibit high crack self-healing performance, even a relatively large crack having a crack width of about 0.3 mm, which has been difficult to self-heal in the past, can be used. By using a cement admixture or a cement composition, it becomes possible to self-heal cracks well.

  The cement admixture and cement composition according to the present embodiment are as described above, but the embodiment disclosed this time should be considered as illustrative in all points and not restrictive. . The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

  A blast furnace slag fine aggregate: an admixture as coating particles using BFS as a carrier (Core) was prepared using the materials shown in Table 1.

As the blast furnace slag fine aggregate (Blast furnace slag sand (BFS) in the table), blast furnace slag fine aggregate BFS 2.5 (maximum particle size 2.5 mm) defined in JIS A5011-1 was used.
Coating material A (Coating A in the table) for coating particle A as the first admixture is composed of 60% alumina cement (Allumina cement (AC)), 20% calcium hydroxide (Calcium hydroxide) (CH), and water (Tap). water) 20% was used.
Coating material B for coating particle B as the second admixture (Corting B in the table) is an early-strength Portland cement (High-strength Portland cement (HC)) 60%, anhydrous gypsum (AN)) 20% and 20% water (Tap water) were used.

Coating particles A and B were produced by the following method.
A carrier (blast furnace slag fine aggregate; BFS) and each coating material were added and subjected to rolling granulation to prepare coated particles having the coating material attached to the surface of the carrier. Rolling granulation is performed using a small bread granulator (pan inner diameter = φ300 mm × depth 120 mm, motor output 10 W) under the conditions of an inclination angle of 45 degrees, a rotational speed of 40 rpm, and a material charge of 1 kg per batch. It was. First, after the whole amount of the carrier (BFS) material was put into the pan, water and powder of the coating material were alternately added little by little while rolling to prepare for 10 minutes. The produced granulated product is consolidated by its own weight, and is put in a polyethylene bag having a length of 700 mm × width of 400 mm × thickness of 0.1 mm in order to prevent the particles from adhering to each other. And sealed for 7 days.
The material composition of the coating particles A (BFS-GA) and B (BFS-GB) was as shown in Table 2.

Next, mortar was produced.
The mortar was blended as shown in Table 3, W / C = 50%, and the mass ratio of cement to fine aggregate = 2.55. The materials shown in Table 1 are used, that is, Cement C is usually Portland cement (Ordinary Portland cement), Fine Aggregate S (fine aggregate) is blast furnace slag fine aggregate, and chemical admixture (chemical admixture) is high performance. An AE water reducing agent (AE high range water reducing admixture (SP)) was used.
A part of the fine aggregate was replaced with coating particles A and / or B for a total of 240 kg / m ³ . SP was regarded as a part of the mixed water including the solid content. The mortar was kneaded for 120 seconds in a constant temperature room at 20 ° C. with a batch mixing amount of 3 liters.
As the mortar, mortar using only BFS as a fine aggregate (BFS-Plane, No. 1), mortar using only coating particles A (BFS-GA (240), No. 2), and only coating particles B were used. Four types of mortar (BFS-GA + GB (240), No. 4) using mortar (BFS-GB (240), No. 3) and coating particles A and B were prepared.

(Fresh test / Compressive strength test)
The mortar temperature, flow value (according to JIS R 5201), and air volume (according to JIS A 1128) immediately after production as described above are measured, and a φ50 mm × h100 mm cylindrical specimen for compressive strength is produced. It was cured by sealing at 20 ° C. until the age of the material.
Table 3 shows the fresh properties and the compressive strength of the mortar.
Mortar (No. 1) using only BFS as fine aggregate, mortar (No. 2) using only coating particle A, mortar (No. 3) using only coating particle B, and coating particles A and B were used. When the flow value of the mortar (No. 4) was measured, when each coating particle was mixed with 240 kg / m ³ , the SP amount was 1.5% by mass, and both were No. The flow value was improved from the mortar of 1, and bleeding was also reduced.
No. Compared to the mortar of 1, the mortar using each coating particle had high compressive strength on the 7th and 28th.
The number of specimens was N = 3 in all tests.

(Water flow test)
Similarly to the specimen for compression test, a specimen for water passage test for evaluating the self-healing performance of cracks was prepared, and the cylindrical specimen was split at the age of 28 days, and lengths were formed at both ends of the splitting surface. After a paraffin film of 100 mm x width 5 mm x thickness 0.3 mm is sandwiched, it is restrained by two steel hose clamps so that the surface cracks on the upper and lower end surfaces of the cylindrical specimen are about 0.2 to 0.3 mm. Adjusted. A PVC pipe of φ50 mm × h100 mm was connected to the upper surface of the specimen so that the water head was about 80 mm (water pressure = about 0.8 kPa), and the connection part was sealed with silicone resin. In the water flow test, a test sample for water flow test was placed vertically on a steel grating in a constant temperature room at 20 ° C, and tap water was continuously poured into a PVC pipe (internal volume = about 157 ml) on the top surface of the test sample. Maintained full water for 60 minutes. Thereafter, the water injection was stopped, and the amount of water leakage for 10 minutes was measured from the full water state to obtain the first amount of water leakage (0 days). Thereafter, the PVC pipe was filled with water once a day, water injection was stopped, and the amount of water leakage for 10 minutes was measured.
The results are shown in FIG.
In order to clarify the change in the amount of water leakage in each specimen, the result of the water flow test is expressed as a ratio to the initial amount of water leakage, and is expressed as a water permeability ratio (permeability ratio:%) in the figure.

As shown in FIG. 1, in the mortar (No. 4) using the coating particles A and B, the water permeability ratio was greatly reduced in the shortest period from the start of water flow.
That is, it is clear that the crack healing performance is the highest.

(Qualitative analysis by powder X-ray diffraction (XRD))
Qualitative analysis by powder X-ray diffraction (XRD) was performed on the following eight types of samples.
・ Alumina cement (AC)
・ Calcium hydroxide (CH)
・ Early strength Portland cement (HC)
・ Anhydrous gypsum (AN)
・ Carrier (BFS)
・ Coating part collected from coating particle A surface before blending into mortar ・ Coating part collected from coating particle B surface before blending into mortar The crack surface of the specimen was split again 14 days after the start of water passage in the water flow test of No. 4 mortar, and a white product (No. 4 mortar compound) generated on the cracked fracture surface was collected using a stainless spatula. Incidentally, the carrier (BFS) from the alumina cement (AC) is all used as a material for the coating particles.
The coated part of the coated particles was collected by putting the particles in an agate mortar, hitting lightly with an agate pestle so as not to crush the BFS in the carrier part, and grinding the coated part. In the pretreatment of the sample for analysis, after hydration was stopped using acetone, the pressure was reduced using a circulation aspirator, and the sample was dried at about 10 to 20 hPa for 6 hours.
The results are shown in Table 4.

As shown in Table 4, the coating portion of the coating particle A having BFS as a core is composed of hydrogarnet (3CaO.Al ₂ O ₃ .6H ₂ O), hydrocalumite (3CaO.Al ₂ O _3. Ca (OH) ₂ .12H ₂ O) and gibbsite (Al (OH) ₃ ) were identified. These are considered to originate from the hydration reaction of the coating material (alumina cement + calcium hydroxide) of the coating particles A. In addition, unhydrated monocalcium aluminate (CaO.Al ₂ O ₃ ) was identified. This is thought to be because the water binding ratio of the coating material A is as small as 25%, which is lower than the theoretical binding water amount (30.4%) necessary for the monocalcium aluminate to be completely hydrated to form hydrogarnet. It is done. On the other hand, since the peak of calcium hydroxide has almost disappeared, as shown in the formula (1), most of the calcium hydroxide is monocalcium aluminate (CaO.Al ₂ O ₃ ) which is a main constituent mineral of alumina cement. ) And changed to hydrocalumite.

CaO.Al ₂ O ₃ + 3Ca (OH) ₂ + 10H ₂ O
→ 3CaO.Al ₂ O ₃ .Ca (OH) ₂ .12H ₂ O (1)

In the coating portion of the coating particle B having BFS as a core, a large peak of calcium hydroxide and a peak of ettringite were identified as hydrates. These are considered to be derived from the hydration of the coating material of coating particles B (early strong Portland cement + anhydrite). In addition, unhydrated cement minerals (C ₃ S, C ₂ S), dihydrate gypsum, anhydrous gypsum, and calcium carbonate were identified. Since the water binding ratio of the coating material B is as small as 25%, there are many unhydrated early-strength Portland cements, and anhydrous gypsum is an excessive amount with respect to the aluminate originally contained in the early-strength Portland cements. It is thought that it remained. In addition, the peak of monosulfate (3CaO.Al ₂ O ₃ .CaSO ₄ .12H ₂ O) was not confirmed.
No. after the water flow test. As for the white deposit of 4 mortar, a slightly large peak of hydrogarnet and ettringite and a small peak of calcium hydroxide were identified as hydrates. Moreover, a small peak of C ₂ S was confirmed as an unhydrated cement mineral. These are considered to be derived from the coating particles A and the coating material of the coating particles A.

Further, the white precipitate had the hydrocalumite peak identified in the coating portion of the coating particle A disappeared. Further, the gypsum peak identified in the coating portion of the coating particle B was also lost. Therefore, as shown in the formula (2), it is considered that hydrocalumite and gypsum reacted in the cracked part during the water flow test to produce ettringite (3CaO.Al ₂ O ₃ .3CaSO ₄ .32H ₂ O).

3CaO.Al ₂ O ₃ .Ca (OH) ₂ .12H ₂ O + 3CaSO ₄ + 20H ₂ O
→ 3CaO.Al ₂ O ₃ .3CaSO ₄ .32H ₂ O + Ca (OH) ₂ (2)

In addition, a small peak of calcium carbonate was identified in the white precipitate of No. 4 mortar after the coating portion of the coating particle B and the water flow test. These are considered to be produced by neutralizing calcium hydroxide with CO ₂ in the atmosphere.

(SEM-EDS, TG-DTA analysis results)
Observation of surface of sample by scanning electron microscope-energy dispersive X-ray spectroscope (SEM-EDS) of coated particles collected from coating particle A and coating particle B and white precipitate of No. 4 mortar after water passage test The hydrated product was analyzed by elemental analysis and thermogravimetric differential thermal analysis (TG-DTA).
FIGS. 2 to 4 show the results of observation and elemental analysis of the sample surface by SEM-EDS.
2 shows the coating portion collected from the coating particle A, FIG. 3 shows the coating portion collected from the coating particle B, and FIG. 4 shows the analysis result of the white precipitate of No. 4 mortar.

From the analysis results of XRD and SEM-EDS, the coating portion of the coating particle A mainly contains calcium aluminate hydrate (hydrogarnet, hydrocalumite), unhydrated monocalcium aluminate, and the like. Conceivable.
From the analysis results of XRD and SEM-EDS, the coating part of the coating particle B is mainly composed of calcium hydroxide, anhydrous gypsum, dihydrate gypsum, calcium carbonate, unhydrated cement mineral (C ₃ S, C ₂ S), etc. It is thought that it is included.
No. after the water flow test. As for the white deposit of 4 mortar, ettringite is identified from XRD. Moreover, the needle-like crystal | crystallization of ettringite was confirmed from SEM-EDS. No. It is considered that the amount of water leakage at the initial stage of the 4-mortar water flow test is related to the formation of ettringite.

In FIG. The result of the thermogravimetric differential thermal analysis (TG-DTA) of the white deposit of 4 mortar is shown. An endothermic peak centered around 105 ° C. was confirmed. This was presumed to be mainly due to dehydration of ettringite, and the heat loss at 15 to 130 ° C. was about 12%. Furthermore, an endothermic peak centered around 292 ° C. was confirmed. This was presumed to be due to dehydration of hydrogarnet, gibbsite, etc., and the heat loss at 130-300 ° C. was about 12%. In addition, the endothermic peak derived from calcium hydroxide and calcium carbonate was hardly confirmed.
As a self-healing technique for cracks for the purpose of preventing water leakage, it is considered important for the self-healing mechanism to generate ettringite having expandability and containing many water molecules in the cracked part.
That is, hydrocalumite or the like is left in the coating portion of the coating particle A, and anhydrous gypsum is left in the coating portion of the coating particle B, and these two kinds of coating particles are mixed in the mortar to form a cracked portion after the water flow test. Ettringite could be generated.

Claims (3)

A first admixture comprising alumina cement and calcium hydroxide;
Portland cement and a second admixture containing calcium sulfate are mixed ,
The first admixture is a granulated body or coating particles formed by attaching alumina cement and calcium hydroxide to the surface of the carrier,
The second admixture is a cement admixture that is a granulated body or coating particles formed by attaching Portland cement and calcium sulfate to the surface of a carrier . It said first admixture and the second admixture is a cement admixture according to claim 1, which is mixed so that the molar ratio of SO ₃ becomes 0.09 or more 3.56 or less for Al ₂ O ₃ . A cement composition comprising the cement admixture according to claim 1 or 2 .